REV. B

AD7676

–14–

RESET

DATABUS

BUSY

CNVST

Figure 12. RESET Timing

For other applications, conversions can be automatically initiated.

If

CNVST is held LOW when BUSY is LOW, the AD7676

controls the acquisition phase and then automatically initiates a

new conversion. By keeping

CNVST LOW, the AD7676 keeps

the conversion process running by itself. It should be noted that

the analog input has to be settled when BUSY goes LOW. Also,

at power-up,

CNVST should be brought LOW once to initiate the

conversion process. In this mode, the AD7676 could sometimes

run slightly faster than the guaranteed limit of 500 kSPS.

DIGITAL INTERFACE

The AD7676 has a versatile digital interface; it can be interfaced

with the host system by using either a serial or parallel interface.

The serial interface is multiplexed on the parallel databus. The

AD7676 digital interface also accommodates both 3 V or 5 V

logic by simply connecting the OVDD supply pin of the AD7676

to the host system interface digital supply. Finally, by using the

OB/

2C input pin, either twos complement or straight binary

coding can be used.

The two signals

CS and RD control the interface. When at least

one of these signals is HIGH, the interface outputs are in high

impedance. Usually,

CS allows the selection of each AD7676 in

multicircuit applications and is held LOW in a single AD7676

design.

RD is generally used to enable the conversion result on

the databus.

CNVST

BUSY

DATABUS

CS = RD = 0

PREVIOUS CONVERSION DATA

NEW DATA

Figure 13. Master Parallel Data Timing for Reading

(Continuous Read)

PARALLEL INTERFACE

The AD7676 is configured to use the parallel interface (Figure 13)

when the SER/

PAR is held LOW. The data can be read either

after each conversion, which is during the next acquisition phase,

or during the following conversion as shown, respectively, in

Figures 14 and 15. When the data is read during the conversion,

however, it is recommended that it be read-only during the first

half of the conversion phase. That avoids any potential feedthrough

between voltage transients on the digital interface and the most

critical analog conversion circuitry.

DATABUS

BUSY

CS

RD

CURRENT

CONVERSION

Figure 14. Slave Parallel Data Timing for Reading

(Read after Conversion)

CS = 0

CNVST,

RD

PREVIOUS

CONVERSION

DATABUS

BUSY

Figure 15. Slave Parallel Data Timing for Reading (Read

during Conversion)

The BYTESWAP pin allows a glueless interface to an 8-bit bus.

As shown in Figure 16, the LSB byte is output on D[7:0] and the

MSB is output on D[15:8] when BYTESWAP is LOW. When

BYTESWAP is HIGH, the LSB and MSB bytes are swapped and

the LSB is output on D[15:8] and the MSB is output on D[7:0].

By connecting BYTESWAP to an address line, the 16-bit data

can be read in two bytes on either D[15:8] or D[7:0].

CS

RD

BYTE

PINS D[15:8]

PINS D[7:0]

HI-Z

HI-Z

HIGH BYTE

LOW BYTE

LOW BYTE

HIGH BYTE

HI-Z

HI-Z

Figure 16. 8-Bit Parallel Interface